docs: def _find_coord_vars(self, ds, refresh=False):
          '''
          Returns a list of variable names that identify as coordinate variables.
  
          The result is cached by the passed in dataset object inside of this
          checker. Pass refresh=True to redo the cached value.
  
          :param netCDF4.Dataset ds: An open netCDF dataset
          :param bool refresh: if refresh is set to True, the cache is
                               invalidated.
          :rtype: list
          :return: A list of variables names (str) that are defined as coordinate
                   variables in the dataset ds.
          '''
          if ds in self._coord_vars and refresh is False:
              return self._coord_vars[ds]
  
          self._coord_vars[ds] = cfutil.get_coordinate_variables(ds)
  
          return self._coord_vars[ds]